There is a demand from operators that firearms, such as automatic and semi-automatic rifles, have increased versatility allowing use of the firearm in different conditions. For example, operation desire to mount and switch between different accessory or peripheral devices to automatic and semi-automatic rifles that aid operator use of the firearm on different conditions. In addition to heightened versatility, operators desire robust construction and ease of operability and maintenance allowing the firearm to be versatile while being easy to use and having minimum maintenance needs even when undergoing harsh use in harsh conditions such as high humidity or high dust. Conventional firearms have not successfully satisfied the demands and desires of operators. U.S. Pat. No. 5,824,943 dated Oct. 20, 1998, discloses an example of a conventional self loading rifle with a gas pressure loading arrangement. The conventional gas pressure loading arrangement disclosed includes a gas cylinder fluidly connected to the bore of the rifle barrel, and a gas piston received in the gas cylinder to define a gas chamber. The gas chamber is readily susceptible to fowling resulting in stoppage of the firearm. The exemplary embodiments of the firearms disclosed herein overcome the problems of conventional firearms as will be further described below.